I always feel like any performance claims are nowhere near my real life experience, not even when talking about synthetic benchmarks.
For example I recently set up an Apache server that returned a 304 response, on an AWS t3.micro instance and with the Apache Benchmark tool I got around 3.5k[0] requests per second. Once I've enabled HTTPS that fell to around 500 requests per second.
From what I've read at the time (because I was aware of the general consensus that they should have comparable performance), there is some type of underlying hardware feature the TLS decryption/encryption routine can use to speed things up, but it's only available in AWS in m3 type instances and above. Read it from a Mozilla (I think) article, that I couldn't find again right now.
[0] that 3.5k/500 rps might be higher for you because I used maxminddb IP mapping on each requests which I'm sure adds some considerable factor to the rps.